MAMMALIA. 



the second the ischium. Each innominate bone on its outer side contains a 

 cup-shaped cavity (into the composition of which enter alike the ihum, pubis, 

 and ischium) known as the acetabuhim ; and with this articulates the femur, or 

 thigh-bone (10), representing the humerus of the tore-limb. Toward the middle 

 of the hinder surface of its shaft this bone frequently bears a bold projecting 

 crest termed the third trochanter. As the humerus articulates with the two 

 bones of the fore-arm, so the thigh-bone articulates with the two bones of the 

 lower leg, of which the larger is known as the tibia (12), and the smaller as the 

 fibula(13). Following these comes the ankle-joint, ortarsus(14), which, like the 

 carpus, is formed of an upper and a lower row of small massive bones ; the two 

 uppermost bones being respectively known as the huckle-bone, or astragalus ; 

 and the heel-bone, or calcaneum. Interiorly the tarsus is succeeded by the 

 metatarsal bones (15), corresponding to the metacarpals in the fore-limb, 

 these being followed by the phalanges of the toes (16), which are similar to 

 those of the front limb. To the first toe of the hind foot the name hallux 

 is often applied. It may be added that when (as in the ruminants) there 

 are only two metacarpals, or metatarsals, which are completely joined 

 together so as to form a single bone, or when (as in the horses) there is 

 originally but a single metacarpal or metatarsal, such bone, whether of dual 

 origin or primarily single, is called a cannon-bone. The knee-cap, or patelhi, 

 (11), is a bone in the tendon of the great muscle of the thigh. 



With regard to the teeth, it has been already stated that in the upper jaw 



'Eiq. 2.— Side View of Tipper aud Lower Human Dentition, with tlie sides of the jaw removed to 

 show the rests of the teeth. The tliree lower teeth with branched roots are the molars ; in front of 

 these are the two premolars, then comes the canine, and, finally, the pair of incisors. 



